Trace Elements in West Virginia Coals

MERCURY (Hg)

Mercury is an environmentally important Clean Air Act, Title III Hazardous
Air Pollutant element of considerable environmental concern because mercury
is highly toxic and extremely volatile during coal combustion.

Geologic Distribution: Mercury in coal appears to occur within
pyrite, sometimes sphalerite, and possibly
organically bound 1. In various U.S. coals a good correlation
was found between mercury and pyritic sulfur 2. Sphalerite
in Illinois coals was shown to contain mercury 3. Some
Russian coals contain considerable Hg in the forms of the mineral cinnabar
(HgS), metallic Hg and in organomercury compounds near areas of mercury
mineralization areas 1. Mean whole coal mercury in West Virginia
coals was 0.19 ppm, and despite published relationships, no statistical
correlation was noted between pyritic sulfur and Hg, but total sulfur and
arsenic correlated slightly with Hg. Mercury, however, did correlate somewhat
with thallium (Tl) on a whole coal basis. Mercury content in West
Virginia coals was generally very low and variable. Upper Pennsylvanian
coals consistently contained 0.1-0.3 ppm mercury. Middle Pennsylvanian
coals exhibited lower mercury contents and Lower Pennsylvanian coals exhibited
low but erratic mercury abundances. Highest Hg content coals were
in thin, high sulfur, and generally unminable upper Allegheny and Conemaugh
group (Lower Kittanning through Harlem: see
the historic coal production) coals in Monongalia, Preston and Mineral
counties (see cautionary note page).

Economic Impact: Future regulations restricting the allowable
amount of mercury in coal used for combustion could possibly impact a few
minor and generally unmined coals in West Virginia. Mercury has a
vast range of important economic uses.

Environmental Impact: There are important natural sources of
atmospheric Hg including volcanoes and hot springs, volatilization from
vascular plants and degassing from land and water 1. Industrial
sources of atmospheric Hg include cremation, cement making, and of course
coal combustion 1. Mercury is volatilized in the combustion
of coal, but varying amounts of Hg are retained in fly ash, resulting in
less atmospheric emission 1.